This invention pertains to electroluminescent displays and, more particularly, is concerned with electroluminescent devices having contrast enhancing dark fields.
One form of electroluminescent (EL) display includes a transparent EL active laminate interposed between a transparent front electrode and a metallic rear electrode. The electrodes are segmented to correspond to the elements of the displays, which may be alphanumeric or a dot matrix.
The EL active laminate may include an EL phosphor layer sandwiched by dielectric layers. U.S. Pat. No. 4,188,565 suggests use of the non-conducting silicon compounds SiO, SiO.sub.2, Si.sub.3 N.sub.4 as dielectric materials.
When the EL laminate is excited by voltage applied between the front and rear electrodes it emits light. Some of this light reflects off the metallic rear electrode. This reduces contrast and the display's legibility. For this reason, it has been suggested to include a so-called dark field layer of light absorbing material between the active laminate and the rear electrode. Cermet and other materials have been suggested, but it has not been realized that a semiconducting material such as silicon can be used as a dark field material.
Provision must be made to prevent haloing or crosstalk between elements of a display. This occurs when some of the current applied to one electrode activates a non-corresponding element.
Furthermore, it is necessary to drive each element of the display separately. For this reason, an individual switching transistor may be associated with each element. The prior art calls for a physically separate driver circuit as, until the present invention, it was not realized that a driver circuit could be made physcially integral with the display.